Dual-phase Systems Research Articles

Joule heating assisted solvothermal growth of C3N4 on carbon paper for effective photothermal-photocatalytic water splitting for hydrogen evolution

Photocatalysis combined with photothermal effect has become a promising process for highly-efficiently production of H2. In this work, C3N4 was solvothermally grown on carbon paper and further construction of vacancies by fast Joule heating treatment. The substrate carbon paper could increase the photothermal evaporation of water, and the fabricated vacancies could accelerate the charge separation. Furthermore, the temperature increased because of the photothermal synergistic effect, which was favorable for the H2 evolution reaction. Based on the above, the CP/SCN-NVs system achieved efficient H2 evolution in deionized water without sacrificial agent and precious metal co-catalysts, with a hydrogen evolution rate of 2248.83 μmol m-2 h−1, which was 41.3 times higher than the C3N4 suspension system. Overall, this work offered a new approach for efficient H2 evolution in photothermal-photocatalytic dual-phase systems.

Developing ultrafine-grained structure with balanced α/γ fraction via underwater friction stir processing enables enhanced wear and corrosion resistance of duplex stainless steel

Further improving the wear and corrosion resistance of duplex stainless steel (DSS) without disrupting the balanced ferrite (α)/austenite (γ) ratio is worth exploring, but very challenging. Here, we explored the feasibility of utilizing solid-state friction stir processing in air (AFSP) and underwater (UFSP) to realize surface modification of DSS. Notably, we successfully developed an ultrafine-grained (UFG) structure with balanced α/γ ratio on the DSS by UFSP, which imparts both enhanced wear and corrosion resistance to the sample surface. Further, the associated microstructure evolution mechanism during FSP of DSS in both environments is systematically elucidated. The simultaneous improvement in both wear and corrosion resistance is well correlated with the resulting microstructure characteristics. This work provides a simple and cost effective pathway to achieve a synergistic increase in the wear and corrosion resistance of DSS. We anticipate that the UFSP should be applicable to many dual-phase metallic systems.

Research on optimizing strength and ductility of HfNbTaZr dual-phase high-entropy alloy by tuning chemical short-range order

Chemical short-range order (CSRO) plays an important role in the mechanical properties of high-entropy alloys (HEAs). However, the research on the effect of CSRO on the mechanical properties of HEAs only focuses on the single-phase systems, which limits the control of mechanical properties for more HEAs by adjusting CSRO. In this work, the different effects of CSRO on the strength and ductility of single-phase and dual-phase HfNbTaZr are studied by the atomic-scale simulations. The results show that there are differences in the CSRO between single-phase and dual-phase systems. The strength of the single-phase system and dual-phase system both decrease by increasing the CSRO, which was caused by the more severe lattice distortion and higher enrichment degree in the Hf-Zr-rich region. A small amount of HCP (Hexagonal Close Packed) structure plays a role in dispersion strengthening, so the dual-phase system with low CSRO has high strength. The distribution of the Hf-Zr-rich region and the proportion of HCP structure are important factors affecting the ductility. The system, with evenly distributed Hf-Zr-rich regions and a small amount of HCP structure, has better strength and ductility.

Giant heterogeneous magnetostriction induced by charge accumulation-mediated nanoinclusion formation in dual-phase nanostructured systems

The fundamental origin of giant magnetostriction in dual-phase nanostructured systems is still under debate in recent years. Previous studies have revealed that the formation of tetragonal nanoinclusions induced the enlargement in local magnetocrystalline anisotropy, leading to a strengthened magneto–elastic coupling coefficient, which was considered to promote magnetostriction. Another key factor of magnetostriction, the influence of the nanoinclusions on the elastic constants of the lattices is, however, still not clear. In this work, we propose a mechanism based on the experimental and theoretical results of binary and rare-earth (RE) doped FeGa single-crystals. Doping traces of RE atoms effectively increase the density of nanoinclusions in the A2 matrix, due to the high selectivity of RE atoms they possess stronger bonding interaction with Fe atoms rather than Ga atoms. As a consequence, the elastic constant c12 significantly increases with the rising density of tetragonal nanoinclusions as opposed to the constant c11, resulting in a remarkable enhancement in magnetostriction due to the immediate relevance between magnetostriction (λ001) and c11−c12. A superior magnetostriction of 390 ppm is obtained in the RE-doped single-crystal due to lattice softening induced by the nanoinclusions. This uncovered mechanism sheds light onto the contribution of RE atoms on the magnetostriction in FeGa single-crystals, and establishes a foundation for developing new-generation dual-phase magnetostrictive materials with unprecedented levels of magnetostriction.

Giant Heterogeneous Magnetostriction Induced by Charge Accumulation-Mediated Nanoinclusion Formation in Dual-Phase Nanostructured Systems

The fundamental origin of the giant magnetostriction in the dual-phase nanostructured systems is under energetic discussion in recent years. Previous studies have revealed that the formation of tetragonal nanoinclusions induced the enlargement in local magnetocrystalline anisotropy, leading to a strengthened magneto-elastic coupling coefficient, which was considered to promote magnetostriction. As the other key factor of magnetostriction, the influence of the nanoinclusions on the elastic constants of the lattices is still unnoticeably. In this work, we propose a mechanism based on the experimental and theoretical results of binary and rare-earth (RE) doped FeGa single-crystals. Doping traces of RE atoms effectively increase the density of nanoinclusions in the A2 matrix, because of the high selectivity of RE atoms so that they possess stronger bonding interaction with Fe atoms rather than Ga atoms. As a sequence, the elastic constant ς 12 significantly increases with the rising density of tetragonal nanoinclusions as opposed to a constant ς 11, resulting in a remarkable enhancement in magnetostriction due to the inversely proportional relationship between magnetostriction (λ 001) and ς 11 - ς 11. A superior magnetostriction of 390 ppm is obtained in the RE-doped single-crystal due to the lattice softening induced by the nanoinclusions. This model sheds light into the contribution of RE atoms to magnetostriction in FeGa single-crystals, and establishes a foundation for developing new-generation dual-phase magnetostrictive materials to achieve unprecedented levels of magnetostriction.

Influence of MgO-Lignin Dual Component Additives on Selected Properties of Low Density Polyethylene.

The presented study describes the application of lignin-based dual component fillers into low-density polyethylene (LDPE) and an examination of their selected properties. The main experimental procedure was focused on the preparation of thin sheet films using polyethylene and its composites with 5% by wt. of fillers: MgO, MgO-lignin dual phase systems with varying amounts of lignin and pristine lignin. Analysis of morphology revealed that elongated voids appeared in the structure for hybrid filler with a higher content of lignin (min. 50% by wt. of lignin versus MgO) and also for pristine lignin. Moreover, the prepared sheets were subjected to the thermoforming process by using the positive forming method (male mold). The thermoforming ability of all composites was evaluated by means of a comparison of wall thickness distribution on thermoformed shapes. The most noticeable percentage of wall thinning occurred for films which consisted of LDPE/MgO-lignin (5:1 wt./wt.) composite. In contrast, the best material arrangement and the highest mean percentage wall thickness were observed in the case of the shape formed with LDPE/MgO-lignin (1:5 wt./wt.). In addition, as part of research studies, the measurements of the contact angle have been conducted. The analysed LDPE films, in particular LDPE/MgO-L, have been recognized as materials with high wettability.

Mass Transport in (La0.8Sr0.2)0.95CrxFe1–xO3−δ–Scandia-Stabilized Zirconia Dual-Phase Composite as a Dense Layer in Oxygen Transport Membranes

Electrical and oxygen-ion transport in the dual-phase composite systems (La0.8Sr0.2)0.95CrxFe1–xO3−δ (LSCrF) (x = 0.3, 0.5, 0.7)–10 mol % Sc2O3–1 mol % CeO2–89 mol % ZrO2 (10Sc1CeSZ) have been inve...

Oxygen Transport of Lscrf-Scsz Based Mixed Conducting Ceramic Composites

Materials for membrane reactors must possess both high ionic and electronic conductivity as well as good stability over a wide range of oxygen partial pressure. In order to improve the oxygen diffusion, substituting elements is an approach commonly adopted to increase vacancy concentration, but it may also reduce the chemical stability of the membrane [1]. Single phase materials, e.g. La1-x Sr x Co1-y Fe y O3-δ (LSCF), have been shown to possess excellent oxygen permeation properties but suffer from dimensional and chemical instabilities under operation. To improve the long-term stability manganese, chromium etc. can substitute for cobalt but this will sacrifice the permeability of a membrane [2]. Alternatively, focus has been shifted onto dual phase materials which consist of one phase as a good ionic conductor and the other phase as a good electronic conductor. Among all the essential criteria, transport properties of the dense composite layer can profoundly affect the membrane performance. Previous transport measurements work have been carried out on La0.8Sr0.2MnO3-δ (LSM)-Yttria-Stabilised Zirconia (YSZ) [3], LSCF-Ce0.9Gd0.1O2-δ [4] etc. dual phase systems, whilst in this work the La1-x Sr x Cr1-y Fe y O3-δ (LSCrF)-Scandia-Stabilised Zirconia (ScSZ) based dual phase composite system has been investigated. Isotopic Exchange Depth Profiling (IEDP)[5] combined with Secondary Ion Mass Spectrometry (SIMS) was performed in this present work to investigate the mass transport in the composite materials. In order to achieve improved performance optimisation strategies have been applied, which include changing doping level and doping elements in the component LSCrF and ScSZ, and using different volume fractions (LSCrF:ScSZ) in the dual phase composites and optimising the microstructures of the dual phase composites. Additionally, the effects of a humidified environment on the diffusion behaviours of both the single phase and dual phase samples have been studied by using pure labelled H2 18O to reflect operating atmospheres. The diffusion coefficient (D*) at 800 ̊C of LSCrF was found to increase dramatically by 3 orders of magnitude compared to a similar experiment under dry conditions indicating an increase of oxygen vacancy concentration whilst ScSZ remains a good ionic conductor in a pure water atmosphere, and moreover the surface exchange coefficient (k) of ScSZ has been improved to 1.54x10-6 cm/s at 800 ̊C while in dry O2 conditions almost no 18O has been exchanged into the sample. An explanation for this behaviour is that electronic species are not required for the surface exchange process in pure water atmosphere [6] so the rate-limiting steps of surface exchange in ScSZ shifts from dissociation and oxygen reduction in the case of pure oxygen to adsorption steps for water. To obtain further understanding of how the surface has changed during the annealing, X-ray Photoelectron Spectroscopy (XPS) and Low Energy Ion Scattering (LEIS) have been performed in order to observe the surface and sub-surface chemistry and compositional information.

Partitioning Behavior of Trichloroethlyene in Cyclodextrin–Water–Granular-Activated Carbon Systems

The purpose of this study was to collect experimental data and develop a mathematical model describing the equilibrium phase distribution of a common organic chemical, trichloroethylene (TCE), among cyclodextrin (CD), water, and granular-activated carbon (GAC). Batch tests and a modified linear regression model were applied to assess the partitioning behavior in this multiphase (CD pseudophase–water–GAC) system. Results showed that CD lowers TCE availability for dissolution in water and adsorption to GAC, demonstrated by reduced TCE partitioning to GAC with increasing CD concentration. Presence of CD does not significantly affect the distribution of TCE between water and GAC. Rescaled Freundlich adsorption isotherms for the GAC–water (CD-free) and GAC–CD solution systems were not significantly different and overlapping normalized isotherms were observed. This is an important indicator that the distribution of TCE within the dissolved and GAC phase is independent of the presence of CD. It further indicates that the distribution within CD–water–GAC systems can be aptly described by standard TCE Freundlich isotherms for water–GAC dual-phase systems and water–CD partitioning coefficients. A linear relationship between the logarithms of apparent Freundlich isotherm coefficients and solubility enhancement factors (R2=0.99) was verified theoretically and experimentally. This study provides important information to optimize the design, assess the performance of GAC treatment systems containing CD solutions, and possibly aid in prediction the lifetime of GAC in a full-scale operation.

Using noble gases measured in spring discharge to trace hydrothermal processes in the Norris Geyser Basin, Yellowstone National Park, U.S.A.

Dissolved noble gas concentrations in springs are used to investigate boiling of hydrothermal water and mixing of hydrothermal and shallow cool water in the Norris Geyser Basin area. Noble gas concentrations in water are modeled for single stage and continuous steam removal. Limitations on boiling using noble gas concentrations are then used to estimate the isotopic effect of boiling on hydrothermal water, allowing the isotopic composition of the parent hydrothermal water to be determined from that measured in spring. In neutral chloride springs of the Norris Geyser Basin, steam loss since the last addition of noble gas charged water is less than 30% of the total hydrothermal discharge, which results in an isotopic shift due to boiling of ≪ 2.5‰ δD. Noble gas concentrations in water rapidly and predictably change in dual phase systems, making them invaluable tracers of gas–liquid interaction in hydrothermal systems. By combining traditional tracers of hydrothermal flow such as deuterium with dissolved noble gas measurements, more complex hydrothermal processes can be interpreted.

Percolation of Diffusionally Evolved Two-Phase Systems

ABSTRACTAlthough the phase fractions in dual phase systems are often compared with the percolation threshold for a randomly-assembled composite, most two-phase systems are non-random by virtue of correlations introduced during processing or as a consequence of microstructural evolution. This study examines the two dimensional percolation threshold in systems with soft impingement, i.e., when the phase distribution is affected by diffusional interactions between growing second phase particles. Phase field modeling is used to simulate the nucleation and growth process, with many simulations conducted at various system sizes and equilibrium phase fractions to obtain percolation probabilities. The value of the percolation threshold in the thermodynamic limit is estimated based on the finite size scaling behavior of the system. The value of the critical exponent ν (the size scaling exponent) is also estimated.

EXCHANGE COUPLING AND DECOUPLING IN A NANOCOMPOSITE SPIN SYSTEM

We studied the exchange coupling and decoupling process in a nanocomposite spin system based on a 3D Heisenberg model by means of Monte Carlo numerical computation simulation. Different from the conventional micromagnetism approach in which finite elements method (FEM) is usually adopted to compute, in a top-down way, the magnetic property of micromagnetic ensemble in micron even nanometer scale our current paper presents a new approach in computing the magnetic property of above nanomagnetic ensemble. Our approach addressed a composite spin lattice structure consisting of both single spin and cluster spin built up from single spin in a bottom-up way. Two species of distinctive spins were taken into account further in order to imitate the magnetic behavior of heterogeneous ensemble. The simulation revealed the influence of exchange coupling constant Jab, the size of cluster spins d and system reduced temperature t upon the exchange coupling and decoupling between component spin phases, respectively. Smaller value of Jab, larger d and lower temperature t usually lead to the decoupling of originally exchange-coupled component phases and the occurrence of a characteristic two-stage shoulder with an inflexion on the demagnetization curve. The results reported here are, to some extent, of universality and applicable to other dual-phase magnetic systems since our simulation simply focus on a pure duplex spin system rather than a specific material, and all physical variables were treated in a reduced form.

Modelling of the influence of dihedral angle, volume fractions, particle size and coordination on the driving forces for sintering of dual phase systems

The equilibrium shape of solid particles in an aggregate immersed in a liquid or in a gas results from the minimization of interface energy. A model is developed for expressing the dependence of the solid–solid and solid–second phase interface areas on the system parameters: phase volume fractions, dihedral angle, particle size and coordination. The model aims at allowing quantitative assessment of the role of these parameters on the driving force for sintering. The representative volume element is a cone of which the apex angle accounts for the average particle coordination. In order to comply with the uniformity of interface curvature, the solid–second phase interfaces are described using the mathematics of the Delaunay surfaces. The results are compared with the solutions obtained by approximating the interface shape by the revolution of an arc of circle around the cone axis. This approximation does not involve a significant loss of precision.

Topological and chemical arrangement of binary alloys during severe deformation

We explore the alloy structures that can evolve in nonequilibrium driven systems, using two-dimensional atomistic simulations of mechanical alloying. By tailoring the intrinsic system thermodynamics we demonstrate the evolution of alloys with various states of topological and chemical ordering, including random solid solutions with both crystalline and amorphous topology, short-range ordered glasses and crystals, and segregated dual-phase systems. Our observations are broadly consistent with the experimental literature for mechanical alloying of binary systems. Further, while most of our results can be rationalized on the grounds of existing theories for either (i) glass formation and stability or (ii) nonequilibrium systems under external driving, we also observe strong correlations between topological and chemical ordering which have not yet been addressed in the context of driven systems.

A model for oxygen consumption in aerobic heterotrophic biodegradation in dual-phase drainage systems

A mathematical model with two kinetics variations was developed for the description of oxygen consumption in aerobic heterotrophic processes in longitudinal aqueous dual-phase systems where biomass is suspended in the liquid and attached on the solid material surface. This pertains to sewers, drains, rivers and certain wastewater treatment reactors. The model parameters were related to the liquid and solid phases, such as suspended biomass concentration X, its maximum growth rate μ max, water volume V, biofilm oxygen up-take rate BUR, and the biofilm covered area WA. The Monod equation-based zero and first order kinetics were applicable depending on organics concentration. Simulation demonstrated the influence of relevant parameters on the oxygen profile. It illustrated that the suspended biomass can play a critically important role, which generally should not be neglected; the relative importance of the two biomass types is system dependent, and can be quantitatively assessed on the basis of the parameters mentioned above. The potential application of the model is discussed.

On the law of mixtures in dual-phase steels

The applicability of the equation of the stress in the ferrite at the ultimate tensile strain to dual-phase steels obtained by heating 1010 and 1020 grades was tested. The law of mixtures describe the tensile strength of 1010 steels provided the dislocation hardening is included. The equation application to other dual phase systems may require modification to account for differences in metallurgical parameters. (FS)